Method for cooking wood to form chemical paper stock



May 15, 1928. 1,670,156

W. H. HOWELL, JR

METHOD FOR COOKING WOOD TO FORM CHEMICAL PAPER STOCK Filed March 5', 1925 uwaargi C ATTORNEY Patented May 15, 1928.

ily bleached.

' methods,

UlTED STATS WALLACE H. HOWELL, JR.

, or wmsnono, NEW YORK.

METHOD FOR COOKING WOOD TO FORM CHEMICAL PAPER STOCK.

Application filed March My invention relates to a method and apparatus to form wood fiber or' stock from wood by the aid of heat and liquid chemicals. More particularly my invention relates to what is generally known in the art as the soda processand the sulphate process. For the sake of convenience in description, I will describe my invention more particu larly with relation'to the soda process.

My invention relates to an improvedprocess and apparatus wherein the cost of manufacture is materially reduced, and the stock is improved, in that the lignin is immediately removed on the completion of the cook, permitting thefibers to be more read- More particularly my invention relates to the method of washing and cleaning the stock immediately after the cook and while still in the digester, thereby avoiding the use of blow pits and wash. pans, with the consequent loss of time and heat incident thereto, and the expense of their upkeep.

My invention further relates to the method and apparatus of immediately withdrawing the spent'liquor from the digester after the cook, and evaporating it, while at its high temperature, preferably by subjecting it to a vacuum, so that it may be more readily concentrated and passed on to the incinerating furnace to be brunt into black ash preparatory to being leached and the leached liquor subsequently used after being causticized.

My invention further relates to recovering and utilizing the steam in the digester, after the cooking has been completed,to further heat. the spent liquor, whi'le the liquor is subjected to a vacuum. Or, this otherwise waste steam of the digester may be utilized to heat fresh water to wash and clean the cooked fiber in the digester.

My invention further relates to certain combinations, sub-combinations, apparatus and details of construction as will be more fully hereinafter described and pointed out in the claims.

Other advantages of my invention will also be described in the specification, and pointed out in the claims and will be'clearly understood by those skilled in the art.

In the accompanying drawing, I have shown one of the figures somewhat diagrammatically. The apparatus illustrated may be usedto carry out my improved method,

though it. is of course to be understood that 5, 1925. serial No. 13,082.

Fig. 2 is a vertical section through my I preferred form of vertical digester;

Fig. 3 1s a horizontal section, substantially on the line 3-3 of Fig. 2;

Fig. 4 is an enlarged detail view of the steam injector. I

. In the common practicenow uniformly used in the art of manufacturing paper pulpfrom wood by the aid of chemicals and heat, the wood is first formed inchips and placed in a digester. i

For each cord of wood chips it requires .900 gallons of caustic soda liquor at 12 degrecs Baum, and about 92% caustic. To cook one cord of wood requires 2,544 pounds of steam. The size of digesters used in different mills varies somewhat, but the amount of liquor used per cord of wopd, and the amount of steam required 'will be approximately the same. These figures are based on welded digesters 7 feet in "diameter, 27 feet long, and cubical chip space of 910.76 cubicfeet. This digester holds 4.25 cords of wood, and it requires 10,812 pounds of steam to cook this digester.

Chips and liquor are put in in about 45 minutes. The head is put on the digester, steam valve opened, and the cooking process begins. I

this time the digester is up to pressure and the liquor stops circulating. To again start the circulation of the liquor a vent pipe is opened to allow the pressure to be lessened at the top of the di'gesters, when circulation of the liquor is renewed. This is done every 45 minutes until the digester is cooked. It takes'about 5 hours time over all, from the time the digester is put on until itis cooked. Thedigester is then blown by opening a 6" valve in the bottom of the digester. The pressure ,in the digester forces the cooked fibre out to' a blow pit, which is simply a large tank which allows the steam to escape to the atmosphere. It takes 10 minutes to empty the contents of a digester to the blow pit. The stock remains in the blow pit until a wash pan is ready to receive it, then the blow pit is opened and the contents of the blow pit is dumped into the-pan. This re- This. continues for two hours. At

quires approximately minutes. The temperature of the stock in the blow pit is about 180 degrees.

As soon as the stock is in the wash pan, which is a small tank with perforated bottom, to allow the liquor to drain from the stock, the liquor is drained to a tank which feeds the evaporators. The temperature of the liquor going to the evaporator-s is about 170 degrees. The evaporator-s take sufficient water out of the liquor so it can be burned in the rotary furnace, and the black soda ash recovered.

The ordinary process of cooking wood loses about 2,200 pounds of steam per cord of wood when the digester is blown into the blow pit as all of the steam is wasted in the atmosphere. Onepound of coal will usually evaporate about 7 pounds of water and the loss of coal is therefore about 314 pounds of coal per cord of wood. I

A further, disadvantage of the present commerical process lies in the fact that the lignin'is not immediately separated from the cooked fiber but passes into the blow pit and from thence into the wash pans where it is only partially separated'since the cooling re sulting from exposure to the air in the wash pans and from the cool or cold liquor and water used in washing the fiber tends to set part of the lignin which is therefore not removed and renders the fiber harder to bleach.

In the apparatus, which I have shown by way of illustration, the vertical digester 1 is divided by the perforated screen plate 2 to form a chip chamber 3 and a liquor chamber 4;. By removing the head 5 the chip chamber 3 of the digester is filled with chips of any suitable wood, either deciduous or coniferous, until it is full. In practice I preferably use deciduous wods as they are more easily cooked and have less rosin, though my invention can be used with, co-

niferous woods if desired. 1 preferably employ poplar wood and the figures given in this specification refer to treating that wood.

After the chip chamber 3 of the digester is filled with chips, caustic soda liquor, as

in the present practice, is fed into the di-v gester in the usual way. The head 5 is then secured and the steam valve 6 in the steam pipe 7 is opened to supply the necessary steam to cook the chips. all'as in the ordinary practice. The cooking process immediately begins and in about two hours the digester is up to pressure; the liquor which has drained into the liquor chamber 4, and which has been circulated by the steam injector 8 in the injector chamber 9 forcing the liquor through the pipes 10, 11 and spray pan 12, ceases to circulate. It is then necessary to open the relief valve 13 in the relief pipe 14 to permit some of the steam to escape so that the circulation of the liquor from the liquor chamber 4, through pipe 11, spray pan 12 and through the chips in the chip chamber 3 may be continued.

The chips are cooked until commercially satisfactory pulp is produced. The time required for cooking varieswith the nature of the wood and with other factors but under ordinary conditions is approximately five.

hours. When the cook is completed the steam valve 6 in the pipe 7 is closed as are the valves 15 and 26. The valves 16 and 28' in the pipe 17 arethen opened and the spent black liquor is permitted to pass immediately, while still at a high temperature, into the evaporator which may be of any suitable form. In the evaporator the black liquor is concentrated by evaporation to the desired degree and is then burnt in a-n'incinerator to form the so-called black wash which contains large amounts of sodium carbonate. The black wash is then leached to recover the carbonate in the usual manner. I have shown in Fig. 2 the liquor pipe 17 connectcd'directly'to any suitable form of evaporator 19. In Fig. l I have shown the pipe 17 connected with the closed liquor reservoir 20 which feeds the pump 21. This pump forces the liquor through the pipe 22 into the evaporator 19. It is to be understood that this spent liquor may be fed directly into the evaporator 19,- or first into a llleservoir as shown diagrammatically in While the spent liquor is being withdrawn from the digester l, the gate valve 32 is open to permit the steam inthe digester 1 to pass through a reducing valve 33 of any suitable construction, and thence into the steam pipe ,31 which connects with the casing 35 of the evaporator 19, to further heat the spent liquor which is passing through the coils 36 in the evaporator and thereby assist in evaporating the spent liquor prior to its passage to the incinerator.

Alny suitable form ofevaporator may be user shown diagrammatically one effect of the well known Yaryan evaporator, now generally used in the trade. The spent liquor passes through coils 36 of one effect, and thence into the chamber 37 where the vapor is taken off by the pipe 38 to a vacuum pump or condenser, the liquid flowing into the liquor chamber 39, and thence through the pipe 40 to the coilof the next effect of the Yaryan evaporator in the manner well understood. in the art, It is, of course, to be understood that any form of evaporator may be employed in.which the spent liquor is either fed directly from the digester at a high temperature, or through intermediate apparatus, such. as a liquor reservoir ,20 and pump 21. Y

In the diagrammatic view shown in Fig. 1 a pipe 42, with a check valve43, is con- For purposes of illustration, I have.

'into pipe 34 and be utilized to heat the coils 36 through which the spent liquor is circulating.

. As soon asall the spent liquor has been. .withdrawn from the digester -1,'valves 16 and 24 are closed and the water valve 25 in the water pipe-26 is opened to permit fresh heated water preferably at about 200 F. to be fed through the spray pan 12 and pass through the cooked fibers to remove the lignin and all trace of the caustic soda. The valve 26 in drain pipe 27 is closed to permit the first run of the wash Water to pass to the evaporator 19 so as to recover the chemicals. After the wash water has become so weak that it does not pay to run it through the evaporator the valve 28 is closed and valve 26 is opened so as to permit the weak wash water to go to waste.

As soon as the fiber has been thoroughly washed the stock outlet valve 29 is operated by the hand wheel 30 to permit the stock tobe flushed, or otherwise forced, out of the digester through the stock outlet pipe 31, where it will pass into a trough and from this pointv will follow through the paper mill to screens to remove shives, uncooked pieces and knots, if any, or to a breaker which will break the stock if it is not suitable for screens, but without passing through a blow pit or wash pans.

I preferably provide my digester with a man hole 44 so that the interior of the digester may be accessible. After the digester has been emptied of its cooked paper stock, in the manner previously described, it is again filled witlrcliips and caustic soda and the valves are suita 1y operated to permit the new charge to be cooked in the manner previously described.

It will, therefore, be seen that by my improi'ed method and apparatus blow pits and wash pans are entirely omitted, together with the steam and other heat losses incident.

and correspondingly efiects saving in time and amount of bleach required in bleaching.

The high temperature of the liquor in the digester at the end of the cook is conserved and utilized in the evaporator, making it unnecessary to use additional steamin the evaporator and increasing the of evaporation very markedly. 7 Further there necessary to cook the wood.

its usual course is a very material saving in the cost of coal it is well known that the steamy condition of the atmosphere in a paper mill, in which vapors from the wash pans are permitted to escape .into the room, rapidly deteriorates the structure and requires frequent repairs and re.- placcments. All this is eliminated by my invention which by utilizing the waste steam and hot vapors insure a more pleasant condition in the mills for the workmen,

making it a more attractive place to work, besides lessening the cost of upkeep of the structure, and entirely eliminating the upkeep of the stock cleaning department with its blow pits and wash pans.

Having thus described this invention in connection with illustrative embodiments thereof, to the details of which I do not desire to be limited, what is claimed as new and what is desired to secure by Letters Patent is set forth in theappended claimsi What I claim is 1. The method of making chemical wood paper stock consisting in cooking the wood with the aid of steam and a chemicalliquor in a digester, and after-the cook, withdrawing the spent liquor and immediately and,

2. The method of cooking 'wood to produce chemical paper pulp which comprises cooking the wood in a digester with the-aid of steam and a chemical liquor, withdrawing the spent liquor into an expansionchamber, separating steam formed by the reduction of pressure, passing the f liquor while used at a high temperature into an evaporator'and utilizing the steam set free in the expansion chamber to evaporate water from the liquor in the evaporator.

3. Themethod of cooking wood to produce chemical paper pulp which comprises cooking the wood in a digester with the aid of steam and a chemical liquor, withdrawing the spentliquor and immediately while at a high" temperature subjecting it to evaporation in an evaporator, passing the steam in the digester at the end of the cook into the" evaporator and through a reducing valve capable of reducing its pressure to substantially the normal. working pressure of the evaporator.

4. A method of making chemical wood paper stockwhich comprises -.cooking the wood with the aid of a chemical liquor .in

-a digester, withdrawing thespent liquor and immediately, without permitting itto cool substantially subjecting it 'to concentration in an evaporator, and washing the pulp while in the digester at a temperature above that at which the lignin sets.

5. A method of making chemical wood paper stock which comprises cooking the wood with the aid of a chemical digester under pressure, withdrawing spent liquor from the pulp in the digester and immediately without substantial cooling, subjecting it to concentration in an evaporator and "using the hot vapors from said digester a a heating medium in the evaporator, and washing the pulp while in the digester at a temperature above that at which lignin becomes 6. A method of making chemical wood paper stock which comprises cooking the wood with the aid of a chemical liquor in a digcster, withdrawing the spent liquor and immediately without permitting it to cool substantially, subjecting it to concentration in' an evaporator, washing the pulp 7. A method of making chemical wood paper stock which comprises cooking the wood with the aid of a chemical digester under pressure, withdrawing spent liquor.

from the pulp in the digester and immediately without substantial cooling, subject-- ing it to concentration in an evaporator and using the .hot vapors from said digester as a heating medium in the evaporator, washing the pulp while in the digester with hot wash liquor at a temperature above that at which lignin becomes set, withdrawing said wash liquor and immediately without substantial cooling subjecting it to-concentration in an evaporator, washing the pulp with hot water at a temperature above that at which lignin sets, withdrawing said second wash liquor and storing said liquor and utilizing it for the first wash step in a succeeding batch.

8. A method of making chemical wood paperstock which comprises cooking the wood with the aid of steam and a chemical liquor in a digester and after the cook withdrawing the spent liquor-and immediately without substantial cooling subjecting it to concentration in an evaporator.

WALLACE H. HOWVELL, JR. 

